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Homework Help: Relative Roughness of pipes

  1. May 11, 2008 #1
    Relative Roughness of pipes!!!

    1. The problem statement, all variables and given/known data

    Here is the Data:

    Reservoir Water Entry Pipeline Pipeline Pipeline
    Number Level Coeff. Length Diameter Roughness
    m [AHD] [m] [m] [mm]
    0 20.665 0.814 432.453 1.222 0.089
    1 17.787 0.544 111.972 1.361 0.147
    2 11.166 0.583 201.258 1.171 0.076

    2. Relevant equations
    I need to solve this three reservoir problem, but I'm stuck in finding the Reynold's number and Friction factor from Relative densities. Relative roughness is just (Pipeline Roughness/Pipe Diameter). From Moody Diagram, the highest Relative roughness is 0.05 and I can't see anything higher than that, but the values I get are all higher than 0.05 for relative roughness.

    3. The attempt at a solution
    Is there a solution to this?
  2. jcsd
  3. May 16, 2008 #2
    Hello Xaan, you're relative roughnesses are smaller than 0.05. Look at the unit of relative roughness and the ones you are given in the table. That should clarify one of your problems. The one for calculating the Reynolds number is something else. Do you know the formula for this? Can you give some more information on how this system looks like? It is a bit unclear for me to understand.
  4. May 16, 2008 #3
    Yes I realised that relative roughnesses have to be smaller than 0.05. I had to go back and double check it from where I got the info from, and they told me the units they used was wrong. Instead of mm, they put m for pipe diameter. lol so I solved it and I go all the dischages and their directions:

    Q1 + Q2 = Q3

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